A method for determining the femoral anchorage point of a cruciate knee ligament is described in European patent specification DE 693 19 212 T2. Measuring an antetorsion angle of a femur is known from US 2007/0161929 A1 and EP 1 787 581 A1. Reference is also made to these documents, which are hereby incorporated into the disclosure, with respect to determining axes and orientations of a body part and assigning reference frames to a body part.